The present invention relates generally to a system and method for acquiring data, and more particularly to a system and method for acquiring the data by converting analog signals received from sensors to digital signals utilizing a variable sampling rate with high resolution and a capability for fast reading of such data.
Analog-to-digital (xe2x80x9cA/Dxe2x80x9d) converters and digital-to-analog (xe2x80x9cD/Axe2x80x9d) converters have recently come into widespread use with the development of suitable process technology and the increase in digital audio, digital video and other applications. Typically, A/D converters convert an analog input signal into digital output samples at a predetermined rate.
One of the limitations of the conventional A/D converters is that they determine the magnitude of a property of the analog input signal at a predetermined precision only at equally spaced temporal intervals. Such process is known as the xe2x80x9cuniform sampling,xe2x80x9d process in which each sample is provided at the output of the A/D converter at the predetermined precision, e.g., an eight-bit sample. Additionally, with the conventional A/D converters, the sample rate at which the A/D converter operates can not be made independent of the master clock signal used for clocking the A/D converter. The sample rate is likely some integer division of the master clock signal. Further, if the property of the analog input signal changes rapidly, the A/D converter has no capacity to provide a less precise sample at a shortened sample rate.
Certain publications relate to devices and systems utilizing particular sampling devices. For example, U.S. Pat. No. 5,619,202 issued to Wilson et al. describes a method and device for performing A/D conversion using sigma-delta modulation of the temporal spacing between samples. The device described in this publication includes a conventional sigma-delta A/D converter and uses a particular procedure to perform non-linear sampling. The non-linear sampling is achieved by sampling, at a constant rate, the A/D conversion stage, and then utilizing a decimator to decimate the digital samples to match the selected output sample rate.
Another conventional system for data acquisition to digitize and store analog data at a selectable sample rate is described in U.S. Pat. No. 6,166,673 issued to Odom. As described in this publication, the analog signal is first passed through an A/D converter with a high sampling rate. Control logic then collects the samples, and distributes the samples to N memory partitions at a reduced rate equal to the original clock frequency divided by N. The N memory partitions are configurable to be enabled or disabled. In particular each memory partition contains only a portion of the converted digital signal, thus allowing a selectable effective sampling rate.
U.S. Pat. No. 4,812,043 to Vanstaen describes a method and apparatus for measuring a physical quantity (such as the thickness of a textile yarn through a feeding machine) using two identical measuring devices. The first measuring device described in this publication outputs an electrical current or voltage which is a function of the value of such physical quantity. Simultaneously, a second identical measuring device measures a reference value for this physical quantity. The first signal is output to an input of an A/D converter with a variable threshold value. The second signal is applied to the other input of the A/D converter (which determines the variable threshold value). The sampling rate may be determined by a physical movement in the yarn feeding system.
One of the objects of the present invention is to provide a data acquisition system and method which can forward samples of an analog signal at various precisions at various clock intervals. This object can be achieved with the exemplary arrangement and method in which a first digital sample related to an analog signal after a first time period is obtained, then a second digital sample related to the analog signal is relieved after a second time period. The second digital sample is produced at an at least one output if the first digital sample and the second digital sample differ by a predetermined threshold.
Another object of the present invention is to provide a data acquisition system which can perform such procedure. Such exemplary system may include a data processing unit which has at least one data input and at least one data output. When executing a computer program, the data processing unit is adapted to obtain a first digital sample related to an analog signal after a first time period, and a second digital sample related to the analog signal after a second time period. Thereafter, the data processing unit can be adapted to compare the second digital sample to the first digital sample, and produce the second digital sample at the at least one data output if the first digital sample and the second digital sample differ by more than a predetermined threshold.
In another exemplary embodiment of the present invention, the data acquisition system also includes an analog to digital converter which has an input and at least one output. The input can be configured to receive an analog signal, and the output may be configured to provide a digital representation of the analog signal. The output is operatively connected to a data input of a data processing unit.